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## HYDRUS 2.x - Introduction to Building 3D-General Domains

A series of a few video tutorials on this page serves as an introduction to more sophisticated modeling of 3D geometries of general shapes. Three basic techniques for creating objects are illustrated here. Generation of an unstructured 3D finite element mesh is also demonstrated, including the use of local refinement and mesh-stretching. Note that the video tutorials given below are related to the domain type “3D-General” and that simpler computational domains (i.e., 3D-Simple and 3D-Layered) are created differently – see Overview of Domain Types in HYDRUS.

### Step 1 - Creating Solids in the Dialog for Copying and Transforming Objects

This video shows how to create a Solid (volume) using a dialogue window that copies objects and carries out their geometric transformations. Copied objects can be automatically linked, thus creating new Curves, Surfaces, and Solids. This method is especially useful when one needs to create multiple copies of an object in a single step. Procedure: - Select Surfaces (including their Points and Curves), from which you want to create Solids (objects).
- In the dialog window for manipulating geometric objects, select the type of transformation and the number of copies.
- Select the option for the automatic linking of copied objects and generate Solids.
Video Tutorial (12 MB) - Download |
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### Step 2 - Creating Solids graphically by extruding selected Surfaces

This tutorial demonstrates the definition of a Solid by extruding a selected Surface. One can generate multiple Solids at the same time if, before running the graphical tool, one selects multiple Surfaces. Direction of extrusion and an exact thickness of a Solid can be specified in the edit boxes. At the same time, one can assign a material number to a Solid, if one uses the option of defining properties on geometric objects. The Solid created this way has boundary surfaces of the type Planar and Quad. If you want to define a Solid bounded by other Surfaces (B-Spline, Rotary, Pipe, TIN, ...), use the procedure described in the following tutorial or in Tutorial 5.03. Video Tutorial (8 MB) - Download |
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### Step 3 - Creating Solids by Boundary Surfaces

This video tutorial serves as an example of the most general way to define 3D domains; namely using the Boundary Surfaces. Boundary Surfaces may be of different types - Planar and/or Curved, and may also be Components (parts of Surfaces) established by cross-sections of their parent Surfaces. In more complex cases (for example, when one Solid is surrounded by other Solids), it is recommended to divide the Domain into Geo Sections (or to use a function “Sections - Cut with rectangle”) and display in the View window only those Surfaces, from which you want to form a new Solid. Then you can conveniently select Surfaces using either rectangle or other forms of selection (selection using a rhomboid or a polygon, or selecting an object in the data tree of the Navigator). It is also possible to switch the View to the wire-frame view (Wire-Frame Model), thereby disclosing objects otherwise hidden behind other objects. When defining a Solid, it is checked that its boundaries are closed. The Solid may include various internal objects - openings, inner Solids, and/or Surfaces, Curves, and Points.Video Tutorial (11 MB) - Download |
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### Step 4 - Generating the FE-Mesh

This video shows the generation of a FE mesh without any further optimization. An automatically selected size of finite elements is used, which is calculated so that the number of elements is in a reasonable range (on the order of tens or hundreds of thousands of elements). However, such an FE mesh need not be appropriate for calculations and it is usually necessary to modify parameters for mesh generation, so that the resulting FE mesh is suitable for a given problem. The basic parameter for generating the FE-mesh is the desired (or targeted) size of finite elements. This size is used everywhere where there is no local FE-mesh refinement specified to adjust this size. At the same time it is worth bearing in mind that FE meshes with a large number of elements (> 1,000,000) are not suitable for calculations on the PC because of a resulting large demand on computational time. Users are advised to read the Notes on Temporal and Spatial Discretization. Video Tutorial (7.5 MB) - Download |
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### Step 5 - FE-Mesh Refinements

This tutorial demonstrates how to refine the FE mesh using the FE-Mesh Refinement. Mesh Refinements can be defined in Points, on Curves, Surfaces, and/or Solids. Created FE-Mesh Refinement object can then be assigned to one or more geometric objects. In this tutorial, the FE-Mesh Refinement is assigned to four different Solids. If you later decide to refine the FE mesh (for example, to change the desired size of finite elements), you can only change the parameters of the FE-Mesh Refinement object and the sizes of the finite elements will be adjusted in all four elements. Even here, however, the principles mentioned in the previous tutorial need to be considered - the FE mesh needs to be fine enough, so that the numerical solution converges, and not too fine, so that calculations do not take too long. Video Tutorial (10 MB) - Download |
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### Step 6 - FE-Mesh Stretching

In this video we demonstrate the option FE-Mesh Stretching. This option can often help us in creating a FE mesh that reflects direction of pressure head (or concentration) gradients and is thus appropriate for calculations. Note that water fluxes in the vadose zone have predominantly vertical direction. Refinement (shrinkage) of finite elements in one direction (usually vertical direction) gives us a sufficiently fine FE mesh in the direction of high gradients and high fluxes. On the other hand, corresponding stretching of finite elements in the other direction provides us with courser discretization in the direction of minimum fluxes and small gradients, thus reducing the overall number of finite elements and subsequently speeding up numerical calculations.Video Tutorial (10 MB) - Download |
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